When transmitters radiate high intensity electromagnetic waves in close proximity to associated receivers with high sensitivities, these receivers can often be saturated, damaged or otherwise affected in a negative manner by the outgoing transmitter energy. This energy leaks, scatters or reflects back into the receiver.
In the electro-optical and infrared (EO/IR) regimes, this problem has conventionally been handled in one of several ways. Each of the following prior art methods may incur the operational penalties described below.
For split path architectures, the hardware for the transmit and receive functions, their optics and apertures, are physically separated. This approach necessarily takes up more physical space since the design must accommodate separate optical paths for the transmit and receive functions. Furthermore, it may imply harsh mechanical tolerances in order to guarantee that both paths continue to remain co-boresighted.
For baffles, barriers or blocks that prevent transmitter energy from scattering or reflecting back into the receiver field of view (FoV) are installed. This approach may alleviate some of the tolerances imparted on the split path design described above, but it also creates two separate, albeit coaxial, channels. This feature may also make auto-boresighting or operational alignment checks impossible. The inability to perform these functions may levy strict alignment and tolerance constraints of its own. Lastly, these baffles may physically occlude portions of the receiver aperture, and therefore lower overall sensitivity.
For spectral filtering, the transmitter wavelength is chosen to reside completely outside of the receiver spectral bandpass or within the blocking band of a notch filter that will sufficiently attenuate the transmitter intensity. This approach is unworkable, by definition, for active tracking systems because the recevier needs to be sensitive to transmitter radiation. It is the illumination of distant objects with transmitter light that the receiver needs to see in the first place.
In passive tracking systems, spectral filtering is possible, but no auto-boresighting or self-alignment checks can be performed. Again, the inability to perform these functions may levy strict alignment and tolerance constraints.
For shuttering, some mechanical means like an iris is employed to temporarily block the receiver FoV while the transmitter emits each pulse. The utility of this approach may be limited by the speed of the physical mechanism as well as its reliability. Mechanical shuttering may be roughly a thousand to a million times slower than the electronic techniques described herein. This speed may be acceptable in some applications but is unacceptable for others.
Finally, for frame dumping, nothing is done to prevent the blinding saturation effects. Instead, receiver frames that have been corrupted by the presence of unwanted transmitter energy are merely ignored. This approach may be used in systems that range gate or in systems that transmit once and then receive many frames. Tracking systems, however, generally require the continual update coordinates derived from receiver frames and therefore do not have the luxury of throwing away data frames.
A method of electronic signal blanking in optical transceivers that overcomes the disadvantages of the prior art is therefore needed.